A well-known problem associated with cardiac signal detection circuitry is that noise is oftentimes mistakenly interpreted as a cardiac signal. Typically, such noise is caused by myopotentials, the physical movement of electrode wires, and/or by high voltage electric fields in nearby power transmission lines.
Present day cardiac signal recognition circuits are virtually all based on fixed accept/reject criteria, such as specific bandpass frequencies or slew rate limits. These approaches are sub-optimal because little or no consideration is given to noise within the passband, nor to the frequently encountered idiosyncracies of a given patient's heart signal, nor to distinguishing between intrinsic and premature ventricular contractions, nor to myocardial changes related to what the patient may be doing; such as exercising, sleeping, etc.
The foregoing indicates that a real need exists for an improved cardiac signal detection system, i.e., one which is capable of automatically (a) recognizing a patient's intrinsic cardiac signal, (b) recognizing and cancelling extraneous noise, and (c) updating its recognition parameters as the patient's electrographic signature and/or the extraneous noise characteristics change with time.
This invention relates generally to a cardiac signal recognition and noise recognition/cancellation technique, and more particularly, to a cardiac sense amplifier network with capabilities for implementing these techniques. Although discussed strictly in the context of implantable pacemakers, the system described herein can be used to advantage in permanent and/or temporary pacemakers, and/or in virtually any system designed to monitor repetitive electrical signals in the presence of noise.